1. Field of the Invention
The present invention relates, in general, to a method for fabricating surface acoustic wave filter packages and, in particular, to a method for fabricating plural surface acoustic wave filter packages at the same time, in which a wafer having plural surface acoustic wave filter chips is mounted on the substrate having plural mounting portions corresponding to SAW filter chips and each SAW filter chip package is separated through two phases.
2. Description of the Prior Art
Surface acoustic wave filters (hereinafter referred to as xe2x80x9cSAW filtersxe2x80x9d) are frequently used in commercial and other applications as RF and IF filters to provide frequency selectivity and other electronic functions. Because the acoustic wave in the SAW filter often propagates along or very near the surface, the SAW filter is generally very sensitive to surface conditions.
On the whole, a protector is provided to the lower side of the SAW filter to form an air gap for protecting the surface of the SAW filter. Subsequently, on a substrate is mounted the protector-attached SAW filter chip along the outer side of which a metal shield layer is provided for excluding external electrical effects from the SAW filter. As a result, a SAW filter chip package is obtained.
As described above, processes for packaging the SAW filter chip sensitive to external effects are very complicated, unlike processes for packaging other devices, and each SAW filter chip package is individually fabricated in accordance with conventional packaging processes.
In order to better understand the background of the present invention, a description will be given of a conventional method for fabricating the surface acoustic wave filter chip package, below.
FIGS. 1a to 1f are schematic cross sectional views illustrating stepwise conventional fabrication of a SAW filter chip package.
With reference to FIG. 1a, a wafer (not shown) having plural SAW filter chips is divided into individual SAW filter chips 3, and a substrate 2 having plural mounting portions corresponding to SAW filter chips is provided. Protectors 5 are attached to a lower side of the SAW filter chip 3, and bumps 4 for flip chip bonding are attached to an upper side of the substrate 2.
Referring to FIG. 1b, each SAW filter chip 3 is mounted on each mounting portions of the substrate 2, and the SAW filter chip is electrically and mechanically connected to a wiring portion of the substrate 2 by flip chip bonding.
Turning now to FIG. 1c, underfills 6 are filled into a space between the substrate and the SAW filter chip. When underfills 6 are filled between the substrate and the SAW filter chip, an active region positioned on a lower side surface of the SAW filter chip is protected by the air gap formed by protectors 5.
Referring to FIG. 1d, fillets 7 are formed in order to improve step-coverages of sides of SAW filter chips. Fillets 7 are composed of an insulating material, and give a gentle slope to sides of the SAW filter chip 3 having the form of a stepped pyramid, so that the metal layer can be easily formed on the SAW filter chip.
With reference to FIG. 1e, after the fillet is formed, the metal shield layer 8 is formed on the outer wall of the SAW filter chip. To secure reliability of the SAW filter chip, an inner metal layer intercepting external electrical effects is formed on an upper side of the chip, and then an outer metal layer for preventing oxidation of the inner metal layer owing to exposure of the inner metal layer to the atmosphere is additionally formed on the inner metal layer.
After forming of the metal shield layer 8 is accomplished, the resulting SAW filter chip package is marked to allow its identification. That is to say, a dark color paste is coated on the metal shield layer 8 to form an identification layer 9, as shown in FIG. 1f. 
As described above, according to a conventional method for fabricating SAW filter chip packages, SAW filter chips are packaged as individual chip units. That is to say, after plural chips on a wafer are divided into individual chips, each chip is mounted on a package substrate, a underfill material is provided to a space between each SAW filter chip and the package substrate, and the step of forming fillets or metal shield layers and a marking step are conducted for individual chip unit. Accordingly, a method for fabricating SAW filter chip packages is very complicated.
Furthermore, when underfill formed around lower sides of flanks of chips, which are adjacent to each other, is connected to adjacent underfill while underfill is formed, metal shield layers may not be coated on portions, in which underfill is connected to adjacent underfill, around lower sides of flanks of chips. Accordingly, underfill should be elaborately formed in the conventional method for fabricating SAW filter chip packages.
Consequently, the conventional method for fabricating SAW filter chip packages is conducted in individual chip units, and so individual steps as well as entire steps are complicated. In particular, as exemplified by the step of forming the metal shield layer to exclude an outside noise and increase reliability of the SAW filter package and the step of forming the fillet, the steps required for the conventional method for fabricating SAW filter chip packages are so complicated as to be not collectively conducted.
Therefore, there continues to be a need for an improved method for fabricating plural surface acoustic wave filter packages, which can guarantee reliability against external effects and be collectively conducted by the wafer unit.
Therefore, it is an object of the present invention to avoid disadvantages of prior arts, and to provide to a method for fabricating plural surface acoustic wave filter packages at the same time, in which a wafer having plural surface acoustic wave filter chips is mounted on the substrate having plural mounting portions corresponding to positions of SAW filter chips and each SAW filter chip package is separated through two phases.